MADRID (AP) - Rafael Nadal has canceled an exhibition match against Novak Djokovic because of knee trouble.

He said doctors have told him to rest for 15 days because of tendinitis, so as to be ready for the London Olympics.

He and Djokovic were scheduled to play on July 14 for charity at Santiago Bernabeu, home of Real Madrid.

"I will now work on my rehab as well as taking some short holidays to resume my practice in 15 days,'' Nadal said in a statement.

SI Apps
We've Got Apps Too
Get expert analysis, unrivaled access, and the award-winning storytelling only SI can provide - from Peter King, Tom Verducci, Lee Jenkins, Seth Davis, and more - delivered straight to you, along with up-to-the-minute news and live scores.